Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $41.39   13.395%   $46.9342   $46.93   $46.95   $46.90  
  Purchase #2 $113.54   11.619%   $126.7322   $126.73   $126.75   $126.70  
  Purchase #3 $59.63   13.391%   $67.6151   $67.62   $67.60   $67.60  
  Purchase #4 $219.55   5.280%   $231.1422   $231.14   $231.15   $231.10  
  Purchase #5 $19.69   9.182%   $21.4979   $21.50   $21.50   $21.50  
  Purchase #6 $187.74   5.115%   $197.3429   $197.34   $197.35   $197.30  
  Purchase #7 $24.53   9.716%   $26.9133   $26.91   $26.90   $26.90  
  7 purchase totals = $666.07       $718.1778   $718.17   $718.20   $718.00